For those of you who are interested in weather updates, knowing wind speed is valuable. Wind speed determines how soon a storm will arrive while also strongly affecting the creation of high and low-pressure areas. Beyond this, measuring wind speed is a vital factor in everything from piloting a plane to conducting an outdoor athletic activity. With so much riding on this measurement, it’s worth knowing how wind speed is determined so you can decide what instrument measures wind speed best for you circumstances.
The Machinery in measuring Wind Speed
The instrument to measure wind speed is called an anemometerand there are five basic types. Each instrument that measures wind speed has its own subcategories along with pluses and minuses that make it better suited to particular situations than other wind speed measuring devices.
These types of wind meters are among the oldest and most easily recognized. In general, they operate by simply having the wind push on them and come in three primary designs.
Types of mechanical anemometers:
Propeller / Vane Anemometers
The oldest form of the wind meters, invented by Italian architect Leon Battista Alberti in 1450, uses a plate mounted on a strip of springy metal that faces into the wind. As wind speed increases, the wind speed instrument is bent back with the change in its angle corresponding to wind velocity. This type is not very accurate and won’t respond to low wind speeds. A variation of this consists of attaching a ping pong ball to a string and determining wind velocity by the angle of the string as the wind pushes the ball.
The classic image of four cups rotating around a vertical pole was made possible by inventor Dr John Thomas Romney Robinson in 1845. Originally, the device would measure wind speed by counting the number of cup rotations over a time interval. This technique was improved upon by the use of electronics for measuring purposes. Electrical components can either provide greater accuracy in counting rotations per time unit or act as a small generator that creates higher wattage as wind speed increases.
Propeller / Vane Anemometers
The use of a fan permits wind direction to be simultaneously determined with a vane since the turbine has to be facing into the wind. A handheld wind speed meter using a miniature fan has an advantage over its larger cousin by always facing into even the lightest wind since you’re the one doing the pointing. Because it’s not permanently outdoors, a handheld wind speed meter isn’t threatened by winter icing.
2. Pressure Tube Anemometers
Another very old approach to measure wind speed is through the use of a pressure tube. First developed by James Lind in 1775, the basic idea is to start with a U-shaped tube and bend one end over to create a horizontal section that faces into the wind. Liquid is placed at the bottom of the tube and wind blowing into the horizontal portion forces the liquid up along the vertical section. Modern versions have replaced the liquid with a flexible membrane that moves in response to the pressure differences while a gauge translates this into wind speed. With no mechanical parts, this instrument that measures wind speed can go for long periods without maintenance.
3. Thermal / Hot Wire Anemometers
These measuring devices are also known as hot wire anemometers. To understand what measures wind speed, in this case, you start with the underlying principle that a flowing wind cools things off. The device includes a thermostat that keeps a heated wire at a steady temperature. As the wind blows across the wire, it’s cooled and more electricity is used to bring it back up to its set temperature. The increased draw of electricity is what measures wind speed.
4. Sound Wave Anemometers
Regarding what tool measures wind speed, there are two answers in this category.
Types of sound wave anemometers:
Acoustic Resonance Anemometers
Because sound needs gas molecules to travel through, the speed and direction of them can affect the speed of the sound waves. Ultrasonic anemometers use this phenomenon to calculate wind speed. This type of anemometer compares the travel time between a sound generator and a receiver to what it should be under the circumstances. The big drawback with what instrument measures wind speed here is that turbulence created by wind flowing around the instrument itself can distort the results. Rainfall can also play havoc with readings.
Acoustic Resonance Anemometers
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While it also uses sound waves, this kind of wind speed instrument takes a different approach by measuring changes in the frequency of the waves as they collide with passing air molecules. Faster winds will cause the sound waves to compress into a higher frequency. These anemometers are compact and very rugged. On the other hand, this type of wind speed instrument is not that accurate.
5. Doppler Laser Anemometers
This system relies on the same idea behind the ultrasonic anemometer except that laser light is what measures wind speed. The laser beam is split in two. One portion is used for reference while the other is aimed at the wind. If the air is rushing towards the measuring beam, the light waves reflecting off it are squeezed into a higher frequency. This is referred to blue shifting. Laser light bouncing off air particles headed away from the detector undergo red shifting to a lower frequency.
The receiving station compares this reflected light to the reference beam to calculate the speed of the moving air. This instrument to measure wind speed is extremely accurate as well as very expensive. It also requires a lot of technical expertise to operate.
Clearly, there’s a lot of ways to figure out wind speed. Some methods may not be that reliable. Others can be pretty costly and involve unwieldy contraptions. “What tool measures wind speed the best?” in our opinion, comes down to cup anemometers for personal weather stations and handheld anemometers for your more mobile needs due to their affordability, reliability, and durability.